Inductor



R. M. HEINTZ Sqpt. 17, 1935.

INDUCTOR Original Filed April 26, 1933 INVENTOR,

v RALPH M HE/NTZ. B f 1 D A TTORNE Y Patented Sept. 17, 1935 UNITEDSTATES PATENT OFFICE INDUCTOR a corporation of Nevada Application April26, 1933, Serial No. 668,073 Renewed March 4, 1935 6 Claims.

- tions.

Among the objects of my invention are: First, to provide an inductancewhose variation with temperature is practically nil; second, to providea coil having a relatively low resistance at radio frequencies; third,to provide a coil which may be cheaply and easily constructed fromreadily obtainable materials; and fourth, to provide a coil which isrigid and self-supporting.

Other objects of my invention will be apparent or will be specificallypointed out in the description forming a part of this specification, butI do not limit myself to the embodiment of my invention hereindescribed, as various forms may be adopted withinthe scope of theclaims.

Referring to the drawing:

Figure 1 is an elevation, and Figure 2 an end view of an inductor madein accordance with my invention, a portion of Figure 1 being cut away inthe drawing toshow the construction.

Figure 3 is a top view of one end of the in ductor shown in Figure 1. I

The inductance of any conductor depends both upon the length of theconductor, upon its crosssection, and particularly upon its dispositionrelative to other conductors with which it is magnetically linked. Theusefulness of an inductor in an oscillating circuit also demands that ithave low resistance. It is further desirable that it be compact, notonly for purely mechanical reasons, but also to reduce accidentallinkages with other circuits. For these reasons it is customary to forminductors as helices or spirals, so that each element of the conductormay be linked magnetically with as many other elements as possible, thusreducing the length and therefore the resistance of conductor requiredto give a given inductance.

All of the materials having high conductivity have also relatively largecoefllcients of thermal expansion. A rise in temperature of the coiltherefore increases its inductance, not merely in direct proportion toits increase in lengthrbut also by increasing the flux linkages with theother turns of the coil.

Where the inductor is made a portion of an oscillating circuit whichmust be operated as of the chemical deposition methods well nearly aspossible at a standard frequency, or one which is used to measurefrequency, as in a wave meter, it is necessary that such coils as thosedescribed be operated under carefully predetermined thermal conditions,in order that errors 5 duegio temperature variations shall not beintroduced. In cases where temperature control boxes will not give therequired results, i. e., in inductances for radio transmitters of suchpower that a material amount oi.v heat is generated in the coilsthemselves, such devices as water-cooling have been introduced tomaintain the temperature substantially constant.

Broadly considered, my invention comprises an inductor wherein aninsulating core having a substantially zero coefficient of thermalexpansion has bonded thereto a plurality of turns of a conductor havinga relatively high coefficient of thermal expansion. I prefer to mold orcut a thread in the exterior surface of a pyrex or quartz cylinder, anddeposit silver on one face of the thread to form the inductor. Thesilver, being closely adherent to the core material, cannot greatlychange its physical proportions, and its inductive effect, therefore, isbut little disturbed by temperature variations.

' In the drawing, which illustrates a preferred form of cylindricalinductor, a cylindrical core 'I is provided with an exterior fiat-toppedthread 2. The core may be molded'from pyrex or quartz, or otherinsulating material having a low coefficient of thermal expansion. Itisdesirable that the threads be molded on the surface, and be anintegral part of the core. At the same time,

contact extensions 44 may be molded at each end of the core cylinder,the outer surface 5 being an extension of the flat top 6 of the thread.

The number of turns, length of cylinder, and diameter is predicated onthe amount of inductance desired, while the depth of the thread will 49depend on the voltage used and length of surface necessary to provideproper guard against surface leakage. These factors, however, are purelymatters of design well known in the art, I to all of which my inventionis adapted.

It is desirable, after a proper core has been provided, to polish theflat top 6 of the thread and otherwise prepare it for a silverdeposit 1. This deposit may be placed on the thread by any 50 known inthe art, and need only be thick enough to carry the current necessaryfor the subsequent plating operation.

The portions of the thread below the exterior surface are not silvered,but on the contrary, are kept free from any conductive material.

Contact is then made to the silver spiral, the core is immersed in aplating bath, and a conductor 8, preferably silver, is electricallydeposited upon the top of the original silver film, until a sufllcientstrip has been formed to properly carry the current needed for thefinished inductor. Plating is then stopped, binding posts 9-9 areinserted in holes I!) in the contact extensions making direct connectionto the silver strip, and the inductor is ready for use.

A modified process may be employed which gives the same results. Thecylindrical core is not threaded, but the exterior surface is polishedand silvered as a whole. The silver is then selec' tively removed toform a continuous spiral con ductor, and electroplated to form theinductor. It is preferable, in this latter case, to cut the core belowthe exterior surface, while removing the silver. "When this is done, thefinished inductor is identical with the inductor formed on a molded coreas first described.

It has been found that such inductors maintain a remarkably uniforminductive effect in spite of temperature variations, the conductor beingfirmly held to a substantially non-expanding core cannot itself expandto increase the inductance. The bond between the silver and the corematerial is sufiiciently strong to prevent any tearing loose of thesilver, the total physical distortion, therefore, being substantiallyiiiilited to the distortion of the core.

While the invention cylindrical inductor, it other forms, such as a iibeing cut on one fo- It may also be do on other than th example on a adazited to a adapted to the thread 1 core material.

it the conductor of the thread, as for ii of the square thread shown.This would give an inductor equivalent to the usual type of inductorusing an edgewise wound ribbon.

I claim:

1. An inductor comprising a cylindrical core of an insulating materialhaving a relatively low coeflicient of thermal expansion, said corehaving a thread cut on the exterior surface thereof, a layer of silverchemically deposited on one surface of said thread, and a second layerof silver 10 electrically deposited on said first layer.

2. An inductor comprising a cylindrical quartz core, said core having athread cut on the exterior surface thereof, a layer of silver chemicallydeposited on one surface of said thread, and a second layer of silverelectrically deposited on said first layer.

3. An inductor comprising a cylindrical pyrex core, said core having athread cut on the exterior surface thereof, a layer of silver chemicallydeposited on one surface of said thread, and a sec- 0nd layer of silverelectrically deposited on said first layer.

4. An inductor comprising a cylindrical core of insulating material,said core having a thread on the exterior surface thereof, a layer ofmetal chemically deposited on one surface of said thread, and a secondlayer of metal electrically deposited on said first layer.

5. An inductor comprising a core of insulal material, a bonding layer ofmetal chemic lly deposited on a surface thereof, and an additior 1 layerof metal electrically deposited on said iirst layer.

6. An inductor comprising a core of insulating material, a relativelythin bonding layer of metal chemically deposited on a surface thereof,and a relatively heavy additional layer of metal electrically depositedon said first layer.

RALPH M. HEIN'l'iE. 40

